... I tried to be an honest cop in a force full of bribe-takers. But as I found out the hard way, police departments are useless at investigating themselves—and that’s exactly the problem facing ordinary people across the country —including perhaps, Ferguson, Missouri, which has been a lightning rod for discontent even though the circumstances under which an African-American youth, Michael Brown, was shot remain unclear.

Today the combination of an excess of deadly force and near-total lack of accountability is more dangerous than ever: Most cops today can pull out their weapons and fire without fear that anything will happen to them, even if they shoot someone wrongfully. All a police officer has to say is that he believes his life was in danger, and he’s typically absolved. What do you think that does to their psychology as they patrol the streets—this sense of invulnerability? The famous old saying still applies: Power corrupts, and absolute power corrupts absolutely. (And we still don’t know how many of these incidents occur each year; even though Congress enacted the Violent Crime Control and Law Enforcement Act 20 years ago, requiring the Justice Department to produce an annual report on “the use of excessive force by law enforcement officers,” the reports were never issued.)

It wasn’t any surprise to me that, after Michael Brown was shot dead in Ferguson, officers instinctively lined up behind Darren Wilson, the cop who allegedly killed Brown. Officer Wilson may well have had cause to fire if Brown was attacking him, as some reports suggest, but it is also possible we will never know the full truth—whether, for example, it was really necessary for Wilson to shoot Brown at least six times, killing rather than just wounding him. As they always do, the police unions closed ranks also behind the officer in question. And the district attorney (who is often totally in bed with the police and needs their votes) and city power structure can almost always be counted on to stand behind the unions....